1. Field of the Invention
The present invention relates to a ribbon feed device, and more particularly it relates to a ribbon feed device for feeding a ribbon mounted on the recording section of a recording apparatus.
2. Description of The Prior Art
In a serial printer such as wire dot printers, wires are impacted upon a recording ribbon impregnated with ink so that ink sticks to a recording paper to obtain a desired printing. With such an apparatus, the same portion of a ribbon is not repetitively used in printing characters, but the ribbon is fed succeedingly to the recording position of the apparatus during the advancement of recording in order to use different portions of the ribbon.
Conventionally, in feeding a ribbon, a method for feeding a ribbon with a motor used exclusively for that purpose has been employed, or a method for feeding a ribbon by power transmitted from the drive system for scanning a carriage back and forth has been employed. Using an exclusive motor however leads to high cost. Therefore, in recent years the latter motor for driving a carriage has been used widely also for feeding a ribbon. FIG. 1 shows the structure of a ribbon feed mechanism of this method.
In FIG. 1, a timing belt represented by numeral 1 is mounted between a pulley 2 and an unrepresented pulley on the right side. Drive power from a motor for example is transmitted to the unrepresented right side pulley, thus scanning a carriage mounted on the timing belt in right and left directions.
The pulley 2 has teeth 2a concentrically formed thereon which mesh with swing gear 6 of a small diameter. The swing gear 6 is mounted on a shaft 5 provided on a swing plate 4 which can swing about a shaft 3 of the pulley 2 and the teeth 2a. Thus, the swing gear 6 can swing in A2 or B2 direction in response to the rotation of the pulley 2 in A1 or B1 direction while the swing gear 6 meshes with the teeth 2a.
Within the swing area of the swing gear 6, gears 8 and 12 having the same number of teeth are rotatably mounted on respective shafts 7 and 11. These gears respectively mesh with gears 10 and 14 having the same number of teeth, the gears 10 and 14 mounted on respective shafts 9 and 13 meshing with each other.
The gear 10 has a spline 10a mounted coaxially thereon. The spline 10a couples with the drive unit of a ribbon cassette disposed above those gears and feeds the ribbon by the amount corresponding to the rotation of the spline 10a. With such construction, as the timing belt 1 is driven in A direction, the pulley 2 rotates in A1 direction. Then, the swing gear 6, while meshing with the teeth 2a, swings in A2 direction to thereby mesh with the gear 8.
Upon meshing of the swing gear 6 with the gear 8, the swing plate 4 is prevented from further swing so that the rotation of the pulley 2 is transmitted to the swing gear 6 and to the gears 8 to 10. That is, the swing gear 6 rotates in A3 direction, the gear 8 in A4 direction, and the gear 10 in A5 direction.
On the other hand, as the timing belt 1 is driven in B direction, the swing gear 6 swings in B2 direction opposite to the above-mentioned direction to thereby mesh with the gear 12. As a result, the rotation of the pulley 2 in B1 direction is transmitted to the gear 10 via the swing gear 6 and the gears 12 and 14. That is, the swing gear 6 rotates in B3 direction, the gear 12 in B4 direction, and the gear 14 in B5 direction. Consequently, the gear 10 rotates in A5 direction the same as the direction described above.
In this manner, irrespective of the direction of movement of the carriage, the gear 10 is always driven to rotate in A5 direction, and the ribbon is fed with the spline 10a to the recording position always in the same direction.
Among the ribbon feed methods which utilize a drive power for moving a carriage, also known is a method using a spring clutch as shown in FIG. 2 and FIGS. 3(A) and (B).
FIG. 2 is a perspective and exploded view of a ribbon feed mechanism using such method. A timing belt 1 for driving a carriage is here coupled to a pulley 22. The pulley 22 has a clutch boss 22a at its upper portion and a teeth section 22b at its lower portion, respectively formed integrally with the pulley 22. The pulley 22 is rotatably mounted on a shaft 28.
The teeth section 22b meshes with a gear 23 having the same number of teeth as of the teeth section 22b, the gear 23 being integrally formed with a clutch boss 23a.
Gears 25 and 26 are coaxially mounted on respected shafts 28 and 29 disposed above the clutch bosses 22a and 23a via clutch springs 24a and 24b having opposite winding directions to each other. The gears 25 and 26 comprise respectively teeth sections 25b and 26b, and clutch bosses 25a and 26a. The clutch bosses 25a and 25b are positioned inside of the clutch springs 24a and 24b.
The gear sections 25b and 26b mesh with a gear 27 having a spline 27a integrally formed therewith for driving a ribbon.
With the construction as above, as the timing belt 1 is driven in A direction, the gear 22 rotates in A1 direction as shown in FIG. 3(A). As a result, the gear 23 rotates in A2 direction. The direction of the rotation is such that the clutch spring 24b is compressed and the clutch spring 24a is released. Therefore, the rotation is transmitted to the gear 27 via the gears 23 and 26. The gear 26 rotates in A2 direction, while the gear 27 rotates in C direction. The gear 25 rotates in idle in A3 direction while receiving a rotation force from the gear 27.
On the other hand, as the timing belt 1 is driven in B direction, the gear 22 rotates in B1 direction and the gear 23 rotates in B2 direction, as shown in FIG. 3(B). Since the direction of the rotation is such that the clutch spring 24a is compressed and the clutch spring 24b is released, the rotation force is transmitted to the gear 27 through the gears 22 and 25, as opposite to the above case. The gear 22 rotates in B1 direction, the gear 25 in B3 direction, and the gear 27 in C direction the same as in the above case. The gear 26 rotates in idle B4 direction.
As seen from the above, the gear 27 is driven always in C direction so that the ribbon is fed in a determined direction to the recording position irrespective of the drive direction of the carriage.
The above two methods have been used widely wherein the drive force for the carriage is utilized for a ribbon feed. With the method of FIG. 1, there are some problems in that the number of components and the occupied plan area are large. Also, with the method shown with FIG. 2 and FIGS. 3(A) and (B), although the number of components is relatively small, a vertical space in the apparatus is required, thereby making it difficult to have a thin apparatus. Furthermore, in order to avoid any clearance for the clutch spring, it is necessary to strictly control the tolerance of dimensions in the thrust direction. Moreover, since a spring will exert a load in a released state, a large, disadvantageous power loss is present.
Still furthermore, the ink ribbon is fed always at a constant speed and in the same direction even if the carriage movement is reversed. Therefore, if the directions of carriage movement and ink ribbon feed are the same, the relative speed between those of the carriage and the ribbon is small. Alternatively, if the directions of carriage movement and ink ribbon feed are opposite, the relative speed becomes very large. Since a large relative speed between those of the ink ribbon and carriage is present, the head on the carriage is liable to scratch the ink ribbon in many cases.